Exhaust gas treatment system having a solid ammonia gas producing material

ABSTRACT

An exhaust gas treatment system for an internal combustion engine is provided, including an exhaust gas conduit, a pressurized vessel, a selective catalytic reduction (“SCR”) device, and a control module. The internal combustion engine has a plurality of pistons and an engine off condition that indicates that the pistons are generally stationary. The exhaust gas conduit is in fluid communication with, and configured to receive an exhaust gas from the internal combustion engine. The pressurized vessel stores a solid ammonia gas producing material. The pressurized vessel is selectively activated to heat the solid ammonia gas producing material into an ammonia gas. The ammonia gas is released into the exhaust gas conduit. The SCR device is in fluid communication with the exhaust gas conduit and is configured to receive the ammonia gas.

FIELD OF THE INVENTION

Exemplary embodiments of the invention relate to exhaust gas treatment systems for internal combustion engines and, more particularly, to an exhaust gas treatment system having a pressurized vessel that is selectively activated to heat a solid ammonia gas producing material into an ammonia gas.

BACKGROUND

The exhaust gas emitted from an internal combustion engine, particularly a diesel engine, is a heterogeneous mixture that contains gaseous emissions such as carbon monoxide (“CO”), unburned hydrocarbons (“HC”) and oxides of nitrogen (“NO_(x)”) as well as condensed phase materials (liquids and solids) that constitute particulate matter (“PM”). Catalyst compositions typically disposed on catalyst supports or substrates are provided in an engine exhaust system to convert certain, or all of these exhaust constituents into non-regulated exhaust gas components.

One type of exhaust treatment technology for reducing CO and HC emissions is an oxidation catalyst device (“OC”). The OC device includes a flow-through substrate and a catalyst compound applied to the substrate. One type of exhaust treatment technology for reducing NO_(x) emissions is a selective catalytic reduction (“SCR”) device that may be positioned downstream of the OC device. The SCR device includes a substrate, having a SCR catalyst compound applied to the substrate.

In one approach, a reductant is typically sprayed into hot exhaust gases upstream of the SCR device. The reductant may be an aqueous urea solution that decomposes to ammonia (“NH₃”) in the hot exhaust gases and is adsorbed by the SCR device. The ammonia then reduces the NO_(x) to nitrogen in the presence of the SCR catalyst. However, the SCR device also needs to reach a threshold or light-off temperature to effectively reduce NO_(x). During a cold start of the engine, the SCR device has not attained the respective light-off temperature, and therefore generally may not effectively remove NO_(x) from the exhaust gases.

Several drawbacks may exist when spraying an aqueous urea solution into the exhaust gas. For example, the tanks that store the aqueous urea may be heavy and bulky, and therefore add weight and cost to a vehicle. Also, during certain operating conditions, such as low ambient temperatures, the aqueous urea solution may become frozen (i.e. below the freezing temperature of the urea solution which is usually at about negative 12° C.). This causes the urea solution to lose the ability to be injected into the exhaust gas stream by an injector. Thus, in order to maintain the effectiveness of the injector, an electrical heater may need to be provided for thawing the urea solution, which also adds weight and cost to a vehicle. Accordingly, it is desirable to provide an efficient, cost-effective approach for effectively removing NO_(x) from the exhaust gas.

SUMMARY OF THE INVENTION

In one exemplary embodiment of the invention, an exhaust gas treatment system for an internal combustion engine is provided, including an exhaust gas conduit, a pressurized vessel, a selective catalytic reduction (“SCR”) device, and a control module. The internal combustion engine has a plurality of pistons and an engine off condition that indicates that the pistons are generally stationary. The exhaust gas conduit is in fluid communication with, and configured to receive an exhaust gas from the internal combustion engine during operation. The pressurized vessel stores a solid ammonia gas producing material. The pressurized vessel is selectively activated to heat the solid ammonia gas producing material into an ammonia gas. The ammonia gas is released into the exhaust gas conduit. The SCR device is in fluid communication with the exhaust gas conduit and is configured to receive the ammonia gas. The SCR device has a SCR temperature profile and a SCR light-off temperature. The control module is in communication with the internal combustion engine and the pressurized vessel. The control module receives a signal indicating the engine off condition. The control module includes a memory for storing a value indicating a target amount of the ammonia gas released into the exhaust gas conduit by the pressurized vessel and loaded on the SCR device. The control module includes control logic for determining if the internal combustion engine is in the engine off condition based on the signal. The control module includes control logic for determining the SCR temperature profile. The control module includes control logic for determining if the SCR temperature profile is below a threshold value if the internal combustion engine is in the engine off condition. The threshold value indicates that the SCR device is a specified amount below the SCR light-off temperature. The control module includes control logic for determining if the pressurized vessel has released the target amount of the ammonia gas into the exhaust gas conduit if the SCR temperature profile is below the threshold value. The control module includes control logic for deactivating the pressurized vessel if the pressurized vessel has released the target amount of the ammonia gas.

The above features and advantages and other features and advantages of the invention are readily apparent from the following detailed description of the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, advantages and details appear, by way of example only, in the following detailed description of embodiments, the detailed description referring to the drawings in which:

FIG. 1 is a schematic diagram of an exemplary exhaust gas treatment system; and

FIG. 2 is a process flow diagram illustrating a method of activating a pressurized vessel to heat a solid ammonia gas producing material into an ammonia gas.

DESCRIPTION OF THE EMBODIMENTS

The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.

Referring now to FIG. 1, an exemplary embodiment is directed to an exhaust gas treatment system 10, for the reduction of regulated exhaust gas constituents of an internal combustion (“IC”) engine 12. The exhaust gas treatment system described herein can be implemented in various engine systems that may include, but are not limited to, diesel engine systems, gasoline engine systems, and homogeneous charge compression ignition engine systems. In the example as illustrated, the engine 12 includes a plurality of pistons 16. For example, the engine 12 may be an eight cylinder or a twelve cylinder engine, however it is to be understood that any number of pistons 16 may be used as well.

The exhaust gas treatment system 10 generally includes one or more exhaust gas conduits 14, and one or more exhaust treatment devices. In the embodiment as illustrated, the exhaust gas treatment system devices include a hydrocarbon adsorber 20, an electrically heated catalyst (“EHC”) device 22, an oxidation catalyst device (“OC”) 24, a selective catalytic reduction device (“SCR”) 26, and a particulate filter device (“PF”) 30. As can be appreciated, the exhaust gas treatment system of the present disclosure may include various combinations of one or more of the exhaust treatment devices shown in FIG. 1, and/or other exhaust treatment devices (not shown), and is not limited to the present example.

In FIG. 1, the exhaust gas conduit 14, which may comprise several segments, transports exhaust gas 15 from the IC engine 12 to the various exhaust treatment devices of the exhaust gas treatment system 10. The hydrocarbon adsorber 20 includes for example, a flow-through metal or ceramic monolith substrate. The substrate can include a hydrocarbon adsorber compound disposed thereon. The hydrocarbon adsorber compound may be applied as a wash coat and may contain materials such as, for example, zeolite. The hydrocarbon adsorber 20 is located upstream of the EHC device 22, the OC device 24, and the SCR device 26. The hydrocarbon adsorber 20 is configured for reducing the emissions of HC during an engine cold start condition when the EHC device 22, the OC device 24 and the SCR device 26 have not heated to the respective light-off temperatures and are not active, by acting as a mechanism for storing exhaust emission components. Specifically, the zeolite-based material is used to store fuel or hydrocarbons during a cold start.

The OC device 24 is located downstream of the hydrocarbon adsorber 20 and may include, for example, a flow-through metal or ceramic monolith substrate that may be packaged in a stainless steel shell or canister having an inlet and an outlet in fluid communication with exhaust gas conduit 14. The substrate can include an oxidation catalyst compound disposed thereon. The oxidation catalyst compound may be applied as a wash coat and may contain metals such as platinum (“Pt”), palladium (“Pd”), perovskite or other suitable oxidizing catalysts, or combination thereof. The OC device 24 treats unburned gaseous and non-volatile HC and CO, which are oxidized to create carbon dioxide and water.

In the embodiment as illustrated, the EHC device 22 is disposed within the OC device 24. The EHC device 22 includes a monolith 28 and an electrical heater 32, where the electrical heater 32 is selectively activated and heats the monolith 28. The electrical heater 32 is connected to an electrical source (not shown) that provides power thereto. In one embodiment, the electrical heater 32 operates at a voltage of about 12-24 volts and at a power range of about 1-3 kilowatts, however it is understood that other operating conditions may be used as well. The EHC device 22 may be constructed of any suitable material that is electrically conductive such as a wound or stacked metal monolith 28. An oxidation catalyst compound (not shown) may be applied to the EHC device 22 as a wash coat and may contain metals such as Pt, Pd, perovskite or other suitable oxidizing catalysts, or combination thereof.

The SCR device 26 may be disposed downstream of the OC device 24. In a manner similar to the OC device 24, the SCR device 26 may include, for example, a flow-through ceramic or metal monolith substrate that may be packaged in a stainless steel shell or canister having an inlet and an outlet in fluid communication with the exhaust gas conduit 14. The substrate may include an SCR catalyst composition applied thereto. The SCR catalyst composition may contain a zeolite and one or more base metal components such as iron (“Fe”), cobalt (“Co”), copper (“Cu”) or vanadium (“V”) which can operate efficiently to convert NO_(x) constituents in the exhaust gas 15 in the presence of a reductant such as ammonia (“NH₃”).

In the example as shown in FIG. 1, a pressurized vessel 40 is provided for storing a solid ammonia gas producing material 42. In one embodiment, the solid ammonia gas producing material 42 is ammonium carbamate or ammonium carbonate. The pressurized vessel 40 is selectively activated to heat the solid ammonia gas producing material 42 into an ammonia gas that is injected or released into the exhaust gas conduit 14. In the exemplary embodiment as shown in FIG. 1, the pressurized vessel 40 includes a plurality of heaters 44 that are located along the side walls 46 of the pressurized vessel 40. In one example, the heaters 44 are 200 Watt resistive elements that act as heaters. The pressured vessel 40 also includes a flash heater 48 that the solid ammonia gas producing material 42 rests upon. A space 50 exists in the pressure vessel 40 between the pressure vessel 40 and the solid gas producing material 42. In one embodiment, the heaters 44 are activated to heat the solid gas producing material 42 to a temperature ranging from about 60° C. to about 100° C. Then, the flash heater 48 may be activated to heat the solid gas producing material 42 to a relatively high temperature (i.e., in one embodiment to about 110° C.). The temperature created by activation of the flash heater 48 creates a decomposition of the solid gas producing material 42 at the interface between the solid gas producing material 42 and the flash heater 48. Specifically, the activation of the flash heater 48 converts the solid gas producing material 42 into an ammonia gas and carbon dioxide (“CO₂”). The mixture of ammonia gas and carbon dioxide are fed through a tube 52 that is connected to the exhaust gas conduit 14. The mixture of ammonia gas and the carbon dioxide are then dosed or released into the exhaust gas conduit 14. Specifically, the ammonia gas and carbon dioxide are released into the exhaust gas conduit 14 and directed towards the SCR device 26.

The pressure vessel 40 also includes a pressure transducer 54 that is used to monitor the pressure of the space 50 located internally of the pressure vessel 40. Specifically, the space 50 eventually reaches a threshold pressure as the solid gas producing material 42 decomposes into the ammonia gas. The threshold pressure indicates the solid gas producing material 42 is being converted into the ammonia gas and carbon dioxide at a rate that results in a steady supply of ammonia gas that is required by the SCR device 26. That is, the pressure vessel 40 includes a normally closed solenoid valve 56 that is opened in the event the pressure transducer 52 detects that the pressure within the space 50 has exceeded the threshold pressure. The opening of the solenoid valve 56 allows for the ammonia gas and carbon dioxide to enter the exhaust gas conduit 14. Thus, the threshold pressure creates the dispersion or gas propagation needed to create a target amount of ammonia gas released into the exhaust gas conduit 14 that is loaded on the SCR device 26. Specifically, in one example, the target amount of ammonia gas may represent a saturation amount of ammonia gas that is stored by the SCR device 26. The saturation amount represents a maximum amount of ammonia gas the SCR device 26 is capable of storing, however it is to be understood that the target amount of ammonia gas may be other quantities as well.

The PF device 30 may be disposed downstream of the SCR device 26. The PF device 30 operates to filter the exhaust gas 15 of carbon and other particulates. In various embodiments, the PF device 30 may be constructed using a ceramic wall flow monolith filter 23 that may be packaged in a shell or canister constructed of, for example, stainless steel, and that has an inlet and an outlet in fluid communication with exhaust gas conduit 14. The ceramic wall flow monolith filter 23 may have a plurality of longitudinally extending passages that are defined by longitudinally extending walls. The passages include a subset of inlet passages that have and open inlet end and a closed outlet end, and a subset of outlet passages that have a closed inlet end and an open outlet end. Exhaust gas 15 entering the filter 23 through the inlet ends of the inlet passages is forced to migrate through adjacent longitudinally extending walls to the outlet passages. It is through this wall flow mechanism that the exhaust gas 15 is filtered of carbon and other particulates. The filtered particulates are deposited on the longitudinally extending walls of the inlet passages and, over time, will have the effect of increasing the exhaust gas backpressure experienced by the IC engine 12. It is appreciated that the ceramic wall flow monolith filter is merely exemplary in nature and that the PF device 30 may include other filter devices such as wound or packed fiber filters, open cell foams, sintered metal fibers, etc.

A control module 60 is operably connected to and monitors the engine 12 and the exhaust gas treatment system 10 through a number of sensors. The control module 60 is also operably connected to the electrical heater 32 of the EHC device 22, the engine 12, and the pressurized vessel 40. An engine off condition occurs if the pistons 16 are generally stationary within the respective cylinders of the engine 12. In the embodiment as shown, the control module 60 is in communication with an ignition switch 70. The ignition switch 70 sends a signal to the control module 60 that is indicative of the engine off condition. Specifically, the ignition switch 70 includes a key-on state and a key-off state, where the key-off state coincides with the engine off condition. In the key-on state, electrical power is supplied to a propulsion system of a vehicle (not shown in FIG. 1). In the key-off state, electrical power is not supplied to the propulsion system. It should be noted that while the terms key-on and key-off are used, a key may not be employed with the ignition switch 70 in some embodiments. For example, in one embodiment the ignition switch 70 may be activated by proximity to a fob (not shown) that is carried by a user instead of a key. Thus, the key-off state exists when power is supplied to the propulsion system and the key-off state exists when power is not supplied to the propulsion system, regardless of whether an actual key is employed. It should also be noted that while an ignition switch 70 is illustrated, other approaches may be used as well to determine the engine off condition.

FIG. 1 illustrates the control module 60 in communication with two temperature sensors 62 and 64 located in the exhaust gas conduit 14. The first temperature sensor 62 is situated upstream of the SCR device 26, and the second temperature sensor 64 is located downstream of the SCR device 26. The temperature sensors 62 and 64 send electrical signals to the control module 50 that each indicate the temperature in the exhaust gas conduit 14 in specific locations.

The control module 60 includes control logic for monitoring the first temperature sensor 62 and the second temperature sensor 64 and for calculating a temperature profile of the SCR device 26. Specifically, the first temperature sensor 62 and the second temperature sensor 64 are averaged together to create the temperature profile of the SCR device 26. The control module 60 includes control logic for determining if the SCR device 26 is below a threshold temperature. The threshold temperature is below a light-off or minimum operating temperature of the SCR device 26 (i.e. in one embodiment the light-off temperature is about 200° C.). Specifically, the threshold temperature is a specified amount below the light-off temperature of the SCR device 26. That is, the SCR device 26 has been cooled to the threshold temperature such that ammonia gas may be stored on the SCR device 26. In one example, the threshold temperature ranges from between 100° C. to about 150° C., however it is understood that the threshold temperature may include other ranges as well.

The control module 60 also includes control logic for determining if the SCR device 26 has the target amount of ammonia gas loaded therein. Specifically, in one embodiment, the control module 60 includes control logic for determining if the engine 12 is in the engine off condition by receiving the signal from the ignition switch 70. In the event that the engine 12 is in the engine off condition, then the control module 60 includes control logic for determining if the temperature profile of the SCR device 26 is below the threshold temperature. That is, the control module 60 includes control logic for determining if the SCR device 26 is cooled to the threshold temperature such that ammonia gas may be stored on the SCR device 26 when the engine 12 is in the engine off condition. In the event that the SCR device 26 is below the threshold temperature, then the control module 60 also includes control logic for determining the amount of ammonia gas that has been released into the exhaust gas conduit 14 by the pressurized vessel 40.

In the event that the control module 60 determines that the SCR device 26 has the target amount of ammonia gas loaded therein, then the control module 60 includes control logic for deactivating the pressurized vessel 40. Specifically, the control module 60 includes control logic for deactivating the flash heater 48, which in turn ceases the decomposition of the solid gas producing material 42 into the ammonia gas and carbon dioxide. This in turn deactivates the dosing or injection of the ammonia gas into the exhaust gas conduit 14. In the event that the control module 60 determines that the SCR device 26 does not have the target amount of ammonia gas loaded therein, the control module 60 includes control logic for continuing to keep the flash heater 48 of the pressurized vessel 40 activated to produce the ammonia gas.

The control module 60 includes control logic for monitoring the pressure transducer 54. The pressure transducer 54 monitors the pressure of the space 50 located internally of the pressure vessel 40. The space 50 eventually reaches the threshold pressure as the solid gas producing material 42 decomposes into the ammonia gas. Once the control module 60 determines that the threshold pressure has been attained, the normally closed solenoid valve 56 is opened. The ammonia gas and carbon dioxide is then released into the exhaust gas conduit 14.

The control module 60 also includes control logic for selectively activating or deactivating the EHC device 22 based on the temperature profile of the SCR device 26. Specifically, if the temperature profile of the SCR device 26 is above the light-off temperature, then the electrical heater 32 is deactivated, and no longer heats the EHC device 22. However, as long as the temperature profile of the SCR device 22 is below the light-off temperature the electrical heater 32 is activated or remains activated, and heat is provided to the SCR device 26.

The control module 60 also includes control logic for monitoring the temperature of the EHC device 22. Specifically, the control module 60 may monitor the temperature of the EHC device 22 by several different approaches. In one approach, a temperature sensor (not shown) is placed downstream of the EHC device 22 and is in communication with the control module 60 for detecting the temperature of the EHC device 22. In an alternative approach, the temperature sensor is omitted, and instead the control module 60 includes control logic for determining the temperature of the EHC device 22 based on operating parameters of the exhaust gas system 10. Specifically, the temperature of the EHC device 22 may be calculated based on the exhaust flow of the engine 12, an input gas temperature of the engine 12, and the electrical power provided to the electrical heater 32. The exhaust flow of the engine 12 is calculated by adding the intake air mass of the engine 12 and the fuel mass of the engine 12, where the intake air mass is measured using an intake air mass flow sensor (not shown) of the engine 12, which measures air mass flow entering the engine 12. The fuel mass flow is measured by summing the total amount of fuel released into the engine 12 over a given period of time. The fuel mass flow is added to the air mass flow rate to calculate the exhaust flow of the engine 12.

The control module 60 includes control logic for determining if the temperature of the EHC device 22 is above a threshold or EHC light-off temperature. In one exemplary embodiment, the EHC light-off temperature is about 250° C. If the temperature of the EHC device 22 is above the EHC light-off temperature, then the control module 60 includes control logic for de-energizing an electrical source (not shown) of the electrical heater 32.

The SCR device 26 stores the ammonia gas during the engine off condition. This is because the SCR device 26 has been cooled to the threshold temperature, which is a specified amount below the respective light-off temperature of the SCR device 16. Thus, the ammonia gas will not react with the SCR catalyst composition that is disposed on the substrate of the SCR device 26 before a cold start of the engine 12. The SCR device 26 continues to store the ammonia gas before a cold start of the engine 12. During the engine on condition, but prior to attaining the light-off temperature, the SCR device 26 generally acts as a NO_(x) adsorber. That is, the SCR device 26 is generally able to adsorb NO_(x) released into the exhaust gas 15 as the engine 12 operates.

The SCR device 26 is eventually heated to the light-off temperature during operation of the engine 12, which generally effectively reduces the amount of NO_(x) in the exhaust gas 15. Specifically, the NO_(x) in the exhaust gas 15 is reduced to nitrogen after light-off of the SCR device 26. As discussed above, in one embodiment the oxidation catalyst compound applied to the EHC device 22 and the OC device 24 may contain metals such as Pt, Pd, or perovskite. These types of oxidation catalysts may convert NO to NO₂ at a relatively high rate during cold start of an engine when compared to some other types of oxidation catalyst compounds that are currently available. The majority of NO_(x) emitted from the engine 12 is in the form of NO, however it should be noted that NO₂ is more easily adsorbed than NO by the SCR device 26. Thus, the conversion of NO to NO₂ at a relatively high rate may facilitate or improve the reduction of NO_(x) in the exhaust gas 15 by the SCR device 26 once the SCR device 26 is heated to the light-off temperature.

The EHC device 22 is also positioned downstream of a front face 74 of the OC device 24 such that hydrocarbons in the exhaust gas 15 do not substantially interfere with the generation of NO to NO₂ by the EHC device 22. In the embodiment as shown, the EHC device 22 is located within the OC device 24. Specifically, the OC device 24 is employed in an effort to treat unburned gaseous and non-volatile HC and CO upstream of the EHC device 22. Hydrocarbons in the exhaust gas 15 may interfere with the conversion of NO to NO₂ by the EHC device 22. Thus, the placement of the OC device 24, or a portion thereof, upstream of the EHC device 22 facilitates reducing the amount of NO_(x) in the exhaust gas 15 by reducing or substantially eliminating hydrocarbons that interfere with NO₂ generation.

Moreover, the hydrocarbon adsorber 20 is configured for reducing the amount of HC that reaches the EHC device 22 and the OC device 24 during a cold start, which also facilitates or improves the reduction of NO_(x) in the exhaust gas 15. The hydrocarbon adsorber 20 acts as a mechanism for storing fuel or hydrocarbons during a cold start. That is, the hydrocarbons are adsorbed by the hydrocarbon adsorber 20 prior to reaching the EHC device 22 and the OC device 24. Thus, the hydrocarbon adsorber 20 may also facilitate reducing the amount of NO_(x) in the exhaust gas 15 by reducing or substantially eliminating hydrocarbons that interfere with NO₂ generation.

A method of operating the exhaust gas treatment system 10 will now be explained. Referring to FIG. 2, an exemplary process flow diagram illustrating an exemplary process of operating the exhaust gas treatment system 10 is generally indicated by reference number 200. Process 200 begins at step 202, where the control module 60 includes control logic for monitoring the engine 12 for an engine off condition. Specifically, referring to FIG. 1, in one embodiment, an engine off condition occurs if the pistons 16 are generally stationary within the respective cylinders. In one exemplary embodiment, an ignition switch 70 is in communication with the control module 60, and is used to indicate if the engine on or engine off condition has occurred, however it is to be understood that other approaches may be used as well to determine the engine off condition. If the engine 12 is not in the engine off condition, process 200 may then terminate. Process 200 may proceed to step 204 in the event the engine 12 is in the engine off condition.

In step 204, the control module 60 includes control logic for monitoring a temperature profile of the SCR device 26. Specifically, referring to FIG. 1, the control module 60 is in communication with two temperature sensors 62 and 64 located in the exhaust gas conduit 14, where the first temperature sensor 62 is situated upstream of the SCR device 26, and the second temperature sensor 64 is located downstream of the SCR device 26. The control module 60 includes control logic for monitoring the first temperature sensor 62 and the second temperature sensor 64 and for calculating a temperature profile of the SCR device 26. Specifically, the first temperature sensor 62 and the second temperature sensor 64 are averaged together to create the temperature profile of the SCR device 26. The threshold temperature is below a light-off or minimum operating temperature of the SCR device 26. Specifically, the threshold temperature is a specified amount below the light-off temperature of the SCR device 26, such that ammonia gas may be stored on the SCR device 26. If the SCR device 26 is above the threshold temperature, process 200 may continue to monitor the temperature profile of the SCR device 26. In the event that the SCR device 26 is below a threshold temperature, process 200 may then proceed to step 206.

In step 206, the control module 60 includes control logic for determining if the SCR device 26 has a target amount of ammonia gas loaded therein. Specifically, the control module 60 includes control logic for monitoring the amount of ammonia gas that has been released into the exhaust gas conduit 14 by the pressurized vessel 40 decomposing the solid gas producing material 42 into an ammonia gas and carbon dioxide. In the event that the control module 60 determines that the SCR device 26 has the target amount of ammonia gas loaded therein, then process 200 may proceed to step 208. In step 208, the control module 60 includes control logic for deactivating the pressurized vessel 40. Specifically, the control module 60 includes control logic for deactivating the flash heater 48 if the flash heater 48 has been activated. Deactivation of the flash heater 48 will cease the decomposition of the solid gas producing material 42 into the ammonia gas and carbon dioxide. This in turn deactivates the dosing or injection of the ammonia gas into the exhaust gas conduit 14. Process 200 may then terminate. In the event that the control module 60 determines that the SCR device 26 does not have the target amount of ammonia gas loaded therein, process 200 may then proceed to step 210.

In step 210, the control module 60 includes control logic for monitoring the pressure transducer 54. The pressure transducer 54 is used to monitor the pressure of a space 50 located internally of the pressure vessel 40 as the space 50 eventually reaches a threshold pressure. The threshold pressure indicates the solid gas producing material 42 is being converted into the ammonia gas and carbon dioxide at a rate that results in a steady supply of ammonia gas that is required by the SCR device 26. That is, the pressure vessel 40 includes the normally closed solenoid valve 56 that is opened in the event the pressure transducer 52 detects that the pressure within the space 50 has exceeded the threshold pressure. Process 200 may then proceed to step 212.

In step 212, the control module 60 includes control logic for determining if the threshold pressure has been attained. In the event that the threshold pressure has not been attained, process 200 may return to step 210, where the control module 60 continues to monitor the pressure transducer 54. In the event the threshold pressure has been attained, process 200 may then proceed to step 214. In step 214, a normally closed solenoid valve 56 is opened. The ammonia gas and carbon dioxide may then enter the exhaust gas conduit 14. Process 200 may then terminate.

While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the application. 

What is claimed is:
 1. An exhaust gas treatment system for an internal combustion engine, the internal combustion engine having a plurality of pistons and an engine off condition that indicates that the plurality of pistons are generally stationary, comprising: an exhaust gas conduit in fluid communication with, and configured to receive an exhaust gas from the internal combustion engine during operation; a pressurized vessel storing a solid ammonia gas producing material, the pressurized vessel selectively activated to heat the solid ammonia gas producing material into an ammonia gas, the ammonia gas being released into the exhaust gas conduit; a selective catalytic reduction (“SCR”) device in fluid communication with the exhaust gas conduit and configured to receive the ammonia gas, the SCR device having a SCR temperature profile and a SCR light-off temperature; a control module in communication with the internal combustion engine and the pressurized vessel, the control module receiving a signal indicating the engine off condition, the control module including a memory for storing a value indicating a target amount of the ammonia gas released into the exhaust gas conduit by the pressurized vessel and loaded on the SCR device, the control module comprising: a control logic for determining if the internal combustion engine is in the engine off condition based on the signal; a control logic for determining the SCR temperature profile; a control logic for determining if the SCR temperature profile is below a threshold value if the internal combustion engine is in the engine off condition, the threshold value indicating that the SCR device is a specified amount below the SCR light-off temperature; a control logic for determining if the pressurized vessel has released the target amount of the ammonia gas into the exhaust gas conduit if the SCR temperature profile is below the threshold value; and a control logic for deactivating the pressurized vessel if the pressurized vessel has released the target amount of the ammonia gas.
 2. The exhaust gas treatment system of claim 1, wherein the control module includes control logic for monitoring a pressure transducer that indicates pressure located internally of the pressure vessel, and wherein the pressure vessel internally attains a threshold pressure.
 3. The exhaust gas treatment system of claim 2, wherein the control module includes control logic for activating the pressurized vessel if the threshold pressure is attained, and if the pressurized vessel has not released the target amount of the ammonia gas into the exhaust gas conduit.
 4. The exhaust gas treatment system of claim 2, wherein the threshold pressure creates the gas propagation required for creating a gas propagation needed to create the target amount of ammonia gas released into the exhaust gas conduit that is loaded on the SCR device.
 5. The exhaust gas treatment system of claim 1, wherein the target amount of ammonia gas is an amount needed to create a saturation amount of ammonia gas that is stored by the SCR device, and wherein the saturation amount represents a maximum amount of ammonia gas the SCR device is capable of storing.
 6. The exhaust gas treatment system of claim 1, further comprising an electrically heated catalyst (“EHC”) device in fluid communication with the exhaust gas conduit and configured to receive the exhaust gas during operation of the internal combustion engine, and selectively activated to produce heat and induce oxidation of the exhaust gas, the EHC device having an oxidation catalyst compound disposed thereon for converting nitrogen oxide (“NO”) to nitrogen dioxide (“NO₂”).
 7. The exhaust gas treatment system of claim 6, further comprising an oxidation catalyst (“OC”) device in fluid communication with the exhaust gas conduit, the OC device having a front face, the OC device adsorbing hydrocarbons and selectively activated to induce oxidation of the hydrocarbons in the exhaust gas during operation of the internal combustion engine, wherein the EHC device is located within the OC device.
 8. The exhaust gas treatment system of claim 7, wherein at least one of the EHC device and the OC device has an oxidation catalyst compound disposed thereon that is one of Palladium (“Pd”), Platinum (“Pt”), and perovskite.
 9. The exhaust gas treatment system of claim 7, wherein the control module includes control logic for selectively activating the EHC depending on if the SCR device has achieved the light-off temperature during operation of the internal combustion engine.
 10. The exhaust gas treatment system of claim 1, further comprising a first temperature sensor and a second temperature sensor in fluid communication with the exhaust gas conduit, the first temperature sensor situated upstream of the SCR device and the second temperature sensor situated downstream of the SCR device.
 11. The exhaust gas treatment system of claim 10, wherein the control module includes control logic for monitoring the first temperature sensor and the second temperature sensor, and a control logic for calculating the SCR temperature profile based on signals from the first temperature sensor and the second temperature sensor.
 12. The exhaust gas treatment system of claim 1, further comprising an ignition switch, wherein the ignition switch sends the signal to the control module that is indicative of the engine off condition.
 13. An exhaust gas treatment system for an internal combustion engine, the internal combustion engine having a plurality of pistons and an engine off condition that indicates that the plurality of pistons are generally stationary, comprising: an exhaust gas conduit in fluid communication with, and configured to receive an exhaust gas from the internal combustion engine during operation; a pressurized vessel storing a solid ammonia gas producing material, the pressurized vessel selectively activated to heat the solid ammonia gas producing material into an ammonia gas, the ammonia gas being released into the exhaust gas conduit, the pressure vessel configured for internally attaining a threshold pressure; a pressure transducer that indicates pressure located internally of the pressure vessel; a SCR device in fluid communication with the exhaust gas conduit and configured to receive the ammonia gas, the SCR device having a SCR temperature profile and a SCR light-off temperature; an ignition switch that sends a signal that is indicative of the engine off condition; and a control module in communication with the internal combustion engine, the pressurized vessel, the pressure transducer, and the ignition switch, the control module including a memory for storing a value indicating a target amount of the ammonia gas released into the exhaust gas conduit by the pressurized vessel and loaded on the SCR device, the control module comprising: a control logic for monitoring the ignition switch for the signal, wherein the control module includes control logic for determining if the internal combustion engine is in the engine off condition based on the signal; a control logic for determining the SCR temperature profile; a control logic for determining if the SCR temperature profile is below a threshold value if the internal combustion engine is in the engine off condition, the threshold value indicating that the SCR device is a specified amount below the SCR light-off temperature; a control logic for determining if the pressurized vessel has released the target amount of the ammonia gas into the exhaust gas conduit if the SCR temperature profile is below the threshold value; a control logic for deactivating the pressurized vessel if the pressurized vessel has released the target amount of the ammonia gas; a control logic for monitoring the pressure transducer for pressure located internally of the pressure vessel; and a control logic for activating the pressurized vessel if the threshold pressure is attained, and if the pressurized vessel has not released the target amount of the ammonia gas into the exhaust gas conduit.
 14. The exhaust gas treatment system of claim 13, wherein the threshold pressure creates the gas propagation required for creating a gas propagation needed to create the target amount of ammonia gas released into the exhaust gas conduit that is loaded on the SCR device.
 15. The exhaust gas treatment system of claim 13, wherein the target amount of ammonia gas is an amount needed to create a saturation amount of ammonia gas that is stored by the SCR device, and wherein the saturation amount represents a maximum amount of ammonia gas the SCR device is capable of storing.
 16. The exhaust gas treatment system of claim 13, further comprising an EHC device in fluid communication with the exhaust gas conduit and configured to receive the exhaust gas, and selectively activated to produce heat and induce oxidation of the exhaust gas during operation of the internal combustion engine, the EHC device having an oxidation catalyst compound disposed thereon for converting nitrogen oxide NO to nitrogen dioxide NO₂.
 17. The exhaust gas treatment system of claim 16, further comprising an OC device in fluid communication with the exhaust gas conduit, the OC device having a front face, the OC device adsorbing hydrocarbons and selectively activated to induce oxidation of the hydrocarbons in the exhaust gas during operation of the internal combustion engine, wherein the EHC device is located within the OC device.
 18. The exhaust gas treatment system of claim 17, wherein at least one of the EHC device and the OC device has an oxidation catalyst compound disposed thereon that is one of Palladium Pd, Platinum Pt, and perovskite.
 19. The exhaust gas treatment system of claim 13, further comprising a first temperature sensor and a second temperature sensor in fluid communication with the exhaust gas conduit, the first temperature sensor situated upstream of the SCR device and the second temperature sensor situated downstream of the SCR device.
 20. The exhaust gas treatment system of claim 19, wherein the control module includes control logic for monitoring the first temperature sensor and the second temperature sensor, and a control logic for calculating the SCR temperature profile based on signals from the first temperature sensor and the second temperature sensor. 